Carbon fuel particles used in direct carbon conversion fuel cells

ABSTRACT

A system for preparing particulate carbon fuel and using the particulate carbon fuel in a fuel cell. Carbon particles are finely divided. The finely dividing carbon particles are introduced into the fuel cell. A gas containing oxygen is introduced into the fuel cell. The finely divided carbon particles are exposed to carbonate salts, or to molten NaOH or KOH or LiOH or mixtures of NaOH or KOH or LiOH, or to mixed hydroxides, or to alkali and alkaline earth nitrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/471,499 filed May 15, 2003 and titled “Method forPreparation of Carbon Fuel Particles for Use in Direct Carbon ConversionFuel Cells.” U.S. Provisional Patent Application No. 60/471,499 filedMay 15, 2003 and titled “Method for Preparation of Carbon Fuel Particlesfor Use in Direct Carbon Conversion Fuel Cells” is incorporated hereinby this reference.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to direct carbon conversion and moreparticularly to carbon fuel particles used in direct carbon conversion.

2. State of Technology

U.S. patent application Ser. No. 2003/0017380 by John F. Cooper et alfor a tilted fuel cell apparatus published Jan. 23, 2003 provides thefollowing state of technology information, “High temperature, moltencarbonate electrolyte, fuel cells have been shown to be an efficientmethod of producing energy particularly when the fuel source is hydrogengas. Carbon as a fuel source in electrochemical cells has beenexplored.” With the use of carbon instead of hydrogen, the efficiency ofthe fuel cell increases dramatically, as a result of 100% theoreticalefficiency and the possibility of full utilization of the fuel in asingle pass through the cell.

U.S. patent application Ser. No. 2002/0106549 by John F. Cooper et alfor a fuel cell apparatus and method thereof published Aug. 8, 2002provides the following state of technology information, “Hightemperature, molten electrolyte, electrochemical cells have been shownto be an efficient method of producing energy particularly when the fuelsource is hydrogen gas. Carbon as a fuel source in electrochemical cellshas been explored.” This patent application teaches the use of carbonparticles wetted with molten salts consisting of mixed alkali and/oralkaline earth carbonates. Very high efficiencies were obtained when thecarbon particles were produced by the pyrolysis of hydrocarbons in sucha manner as to produce disordered or “turbostratic” materials, having abasis graphitic structure but with small dimensions of the domains ofmicrocrystallinity and with increased average spacing between thegraphene planes.

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides a system for preparing particulate carbonfuel and using the particulate carbon fuel in a fuel cell. Carbonparticles are finely divided. The finely dividing carbon particles areintroduced into the fuel cell. A gas containing oxygen is introducedinto the fuel cell. The finely divided carbon particles are exposed tocarbonate salts, or to molten NaOH or KOH or LiOH or mixtures of NaOH orKOH or LiOH, or to mixed hydroxides, or to alkali and alkaline earthnitrates. One embodiment of the present invention provides an apparatusthat utilizes carbon particles fuel in a fuel cell comprising a fuelcell structure, structure that allows finely divided carbon particles tobe introduced into the fuel cell structure, structure that allows a gascontaining oxygen to be introduced into the fuel cell structure, andstructure that allows the finely divided carbon particles to be exposedto carbonate salts, or to molten NaOH or KOH or LiOH or mixtures of NaOHor KOH or LiOH, or to mixed hydroxides, or to oxidants such asatmospheric oxygen or alkali and alkaline earth nitrates.

The system has uses in efficient electric power generation and in broadmobile, transportable and stationary applications. The system also hasuses in electric power generation at high efficiencies from coal,petroleum derived fuels, petroleum coke, and natural gas. The system canhelp to conserve precious fossil resources by allowing more power to beharnessed from the same amount of fuel, can help improve the environmentby substantially decreasing the amount of pollutants and carbon dioxideemitted into the atmosphere per kilowatt-hour of electrical energy thatis generated, and can help decrease emissions of carbon dioxide, whichare largely responsible for global warming.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 shows one embodiment of a carbon air fuel cell constructed inaccordance with the present invention.

FIG. 2 shows a tilted electrochemical cell to promote rapid draining ofexcess electrolyte constructed in accordance with the present invention.

FIG. 3 illustrates a method of using a ball mill to contact carbon, saltand atmospheric oxygen in a rotating drum.

FIG. 4 illustrates a method of treating particulate carbon, in slurry ofmolten alkali or alkaline earth hydroxides, with oxidation by spargedair.

FIG. 5 shows an arrangement of fuel cell and exiting vapors from themolten salt in the fuel cell to allow contacting between the salt vaporsand the incoming carbon particles.

FIG. 6 illustrates another embodiment of a carbon air fuel cellconstructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, to the following detailed description,and to incorporated materials, detailed information about the inventionis provided including the description of specific embodiments. Thedetailed description serves to explain the principles of the invention.The invention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Referring now to FIG. 1, an embodiment of a fuel cell system constructedin accordance with the present invention is illustrated. The system isdesignated generally by the reference numeral 100. The system 100provides a direct carbon conversion fuel cell that generates electricpower from the electrochemical reaction of carbon and atmosphericoxygen.

Direct carbon conversion fuel cells a method of producing electricity ina fuel cell having an anode and a cathode current collector, an anodefuel consisting of particulates of carbon wetted or contacted withmolten salt (mixtures of alkali or alkaline earth carbonates attemperatures above their melting point), and a means of flowing airadjacent to the cathode current collector, this collector being a highsurface are porous metal structure made of, for example, sintered nickelparticles coated with lithium-doped nickel oxide; silver, copper, goldor other metal providing for the electrochemical reduction ofatmospheric oxygen.

The particulate carbon fuels introduced into the fuel cell must becomewetted with the molten salt. For some carbon fuels (such as raw coal,petroleum coke, and coked or devolatilized coal), the surfaces arecovered with chemical functional groups such as carboxylates, esters,quinoidal, or hydroxyl groups. These groups are readily ionized byamodic oxidation in the presence of molten salts. In the ionized state,they are chemically compatible with the molten salt and are thereforereadily wetted by the salt upon contact between the particles and themolten salt resident in the fuel cell.

Other particulate carbon fuels include very pure carbons such as, forexample, (1) very pure carbons produced by pyrolysis of hydrocarbons(such as, for example, low-sulfur fuel oil, methane, ethane, propane andhigher straight or branched alkanes); (2) acetylene black; (3) furnaceblacks and carbon blacks; (4) the thermal decomposition products of anysaturated hydrocarbon alkane, alkene or alkyne; and (5) carbon aerogelsmade by thermal decomposition of the base-catalyzed condensationproducts of resorcinol with formaldehyde. The surfaces of these verypure materials may tend to be free of ionizable functional groups.Therefore wetting will not readily occur upon contact between the carbonand the molten carbonate salt.

The system 100 provides a method for preparing a particulate carbon fuelfor the fuel cell and a method of introducing the particulate carbonfuel into the fuel cell in a manner allowing a rapid startup of theelectrochemical reaction that produces electric power. The system 100 isuseful in preparing particulates of very pure carbon, such as previouslydescribed.

A process, called direct carbon conversion, has been convincinglydemonstrated. U.S. patent applications No. 2002/0106549 published Aug.8, 2002 and No. 2003/0017380 published Jan. 23, 2003 by John F. Cooperet al show high temperature, molten electrolyte electrochemical cellsfor directly converting a carbon fuel to electrical energy. Thedisclosures of U.S. patent applications Nos. 2002/0106549 and2003/0017380 are incorporated herein by this reference.

With the system 100, it is possible to introduce into the fuel cellparticulates of highly reactive fuels that are made of substantiallypure carbon, and allow these particles to rapidly become wetted andbegin the electrochemical reaction that produces electric power.

The system 100 enables use of large quantities of carbon blacks producedindustrially to be used directly in carbon conversion fuel cells,without laborious and energy intensive mixing of carbon and carbonate.

The system 100 comprises a fuel cell housing 101 containing an anode 105and a cathode 106. A paste, slurry or wetted aggregation 102 isintroduced into the fuel cell housing 101. The paste, slurry, or wettedaggregation of carbon particles 102 comprises carbon particles 104immersed in a molten-salt electrolyte 103 and contained within the anodechamber part of the cell 114.

The carbon 104 is in the form of finely divided particles, typical size100-1000 micrometers, having a reactive nano-structure called“turbostratic.” The carbon particles are immersed in a molten-saltelectrolyte 103 consisting of a mixture of molten alkali carbonates(Li,K,Na)₂C0₃ to form a paste, slurry or wetted aggregation ofparticles.

The slurry 102 is introduced into the fuel cell housing 101. The moltensalt electrolyte 103 provides a continuous electrolyte of carbonparticles 104 between the porous nickel plate anode current collector105 and a porous nickel plate cathode 106. An inert ceramic separator107 (e.g., woven fabrics or felts comprised of alumina or zirconiafibers) saturated with the molten salt may be located between anode 105and cathode 106. The anode current collector 105 and the cathode 106produce an electrical potential between the anode lead 108 and thecathode lead 109, from which electrical current may be drawn by closingthe circuit through a load (not shown). The fuel cell also providesports for introduction of air plus carbon dioxide 110 and exhaust of airand unreacted carbon dioxide 111. The fuel cell also provides at leastone port for exhaust of carbon dioxide reaction product, 112, from theanode chamber; and for the draining of excess molten carbonate from theanode chamber (or introducing additional molten carbonate into thesystem), designated by 113.

The fuel cell system 100 reactions are as follows:

-   -   C+2C0₃ ²⁻=3C0₂+4e− (anodic half-reaction, at an inert current        collector)    -   O₂+2C0₂+4e−=2C0₃ ²⁻ (cathode half-reaction, at Ni0-coated Ni        cathode)    -   C+0₂=C0₂ (Net cell reaction, sum of the half reactions.)

The fuel cell 100 uses aggregates of fine (10- to1,000-micrometer-diameter) carbon particles 104 distributed in, forexample, a mixture of molten lithium, sodium, or potassium carbonate ata temperature of 650 to 850° C. The overall cell reaction is carbon andoxygen (from ambient air) forming carbon dioxide and electricity. Thereaction yields 80 percent of the carbon-oxygen combustion energy aselectricity—approximately 7.2 kWh/kg-carbon. It provides typically up to2 kilowatt of power per square meter of cell surface area—a ratesufficiently high for practical applications. Yet no direct combustionof the carbon takes place. Electrochemical losses within the cell alsoevolve nearly 20% of the combustion energy as waste heat.

The fuel cell 100 is refueled by, for example, entrainment of the finecarbon particles 104 into the cell housing 101 in a gas such as carbondioxide or nitrogen in such a manner that the carbon particles 104 areimmediately wetted by the molten salt upon contact with the ambientmolten salt within the anode chamber, and thus wetted, remain inelectrical contact with the melt until consumed by anodic oxidation.

The system 100 has uses in efficient electric power generation and inbroad mobile, transportable and stationary applications. The system 100also has uses in electric power generation at high efficiencies fromcoal, petroleum derived fuels, petroleum coke, and natural gas. Thesystem 100 can help to conserve precious fossil resources by allowingmore power to be harnessed from the same amount of fuel, can helpimprove the environment by substantially decreasing the amount ofpollutants emitted into the atmosphere per kilowatt-hour of electricalenergy that is generated, and can help decrease emissions of carbondioxide, which are largely responsible for global warming.

The carbon-air fuel cell gives off a pure stream of carbon dioxidethrough port 112 that can be captured without incurring additional costsof collection and separation, as required from the exhausts of smokestacks. The stream of carbon dioxide, already only a fraction of currentprocesses, can be sequestered or used for enhanced oil and gas recoverythrough existing pipelines. Pyrolysis—the thermal decomposition methodused to turn hydrocarbons into hydrogen and tiny pure carbon particlesused in direct carbon conversion—consumes less energy and requires lesscapital than the electrolysis or steam-reforming processes required toproduce hydrogen-rich fuels. Pyrolysis produces millions of tones ofcarbon blacks annually in the U.S. Carbon black is a disordered form ofcarbon produced by thermal or oxidative decomposition of hydrocarbonsand is used to manufacture many different products, including tires,inks, and plastic fillers. A large fraction of the annual production is“off spec”—meaning unsuitable for applications requiring specific size,color, functional groups, conductivity, etc., and is available as a lowcost fuel.

Referring now to FIG. 2, another embodiment of a fuel cell systemconstructed in accordance with the present invention is illustrated. Thesystem is designated generally by the reference numeral 200. The fuelcell system comprises a fuel cell body 201, an anode 205 in the fuelcell body 201, a cathode 206 in the fuel cell body 201, a molten mixtureof alkali- or alkaline earth metal carbonates electrolyte 202 in thefuel cell body 201, and a carbonaceous fuel 204 in the fuel cell body201. The fuel cell system 200 produces electricity with a molten mixtureof alkali metal or alkaline earth metal carbonates and finely dividedcarbon particles. The particulate carbonaceous fuel is introduced intothe fuel cell and produces the direct electrochemical conversion ofcarbon into electricity. A particulate carbonaceous fuel is prepared byfinely dividing carbon particles and mixing the carbon particles with anelectrolyte comprising a molten mixture of alkali metal or alkalineearth metal carbonates.

The system 200 provides a direct carbon conversion fuel cell thatgenerates electric power from the electrochemical reaction of carbon andatmospheric oxygen. A slurry or wetted aggregation 202 is introducedinto the fuel cell housing 201. The slurry 202 comprises carbonparticles 204 immersed in a molten-salt electrolyte 203.

The carbon 204 is in the form of finely divided particles, size 10-1000micrometers, having a reactive nano-structure called “turbostratic.” Thecarbon particles are wetted by a molten-salt electrolyte 203 consistingof a mixture of molten alkali carbonates (Li,K,Na)²C0³ to form a slurry,dense paste or wetted aggregation of particles.

The molten salt electrolyte 203 provides a continuous electrolyte ofcarbon particles 204 between the porous nickel plate anode currentcollector 205 and a porous nickel plate cathode 206. An inert ceramicseparator 207 (e.g., woven alumina or zirconia fibers) saturated withthe molten salt is located between anode 205 and cathode 206. The anodecurrent collector 205 and the cathode 206 produce an electrical current208 in a circuit 209 that extends between anode 205 and cathode 206. Theelectrical current 208 is used to power a device 210 within the circuit209.

The carbon particles 204 can be distributed pneumatically to individualcells, such as cell housing 201, by a small amount of carbon dioxide fedback to the cell from the continuously produced carbon dioxide stream.The pneumatic transport of carbon particles through complex equipment isa widespread industrial practice. The carbon particles 204 and oxygen(ambient air) are introduced as fuel and oxidizer, respectively. Theslurry 202 formed by mixing the carbon particles 204 with moltencarbonate 203 constitutes the anode 206. The anode reaction is carbonand carbonate ions forming carbon dioxide and electrons. At the cathode205, which is similar to that used in other high-temperature fuel cells,oxygen, carbon dioxide, and electrons from the anode form carbonateions. The porous ceramic separator 207 holds the melt in place andallows the carbonate ions to migrate between the two compartments.

Excess electrolyte may drain and flow through port 211 where it isstored as a liquid 212 in a sump 213. By capillary forces, the liquid inthen sump may exchange with that in the slurry and flow backwardsthrough port 211. The system 200 provides a tilted electrochemical cellto promote rapid draining of excess electrolyte, as required to form andmaintain a catalytic surface on the nickel cathode.

The driving force for energy production, called electromotive force,does not degrade as the carbon 204 is progressively consumed to makepower and carbon dioxide, so the voltage remains constant. That meansthat in making a single pass through the cell, all the carbon isconsumed at a maximum yet constant voltage.

The fuel cell system 200 reactions are as follows:

-   -   C+2C0³ ²⁻=3C0²+4e− anodic half-reaction, at an inert (e.g., Ni)        current collector    -   O₂+2C0₂+4e−=2C0₃ ²⁻ cathode half-reaction, at a Ni0-coated Ni        cathode    -   C+02=C02 Net cell reaction, sum of the half reactions

The fuel cell 200 uses aggregates of fine (10- to1,000-micrometer-diameter) carbon particles 204 distributed in a mixtureof molten lithium, sodium, or potassium carbonate at a temperature of650 to 850° C. The overall cell reaction is carbon and oxygen (fromambient air) forming carbon dioxide and electricity. The reaction yields80 percent of the carbon-oxygen combustion energy as electricity. Itprovides up to 2 kilowatt of power per square meter of cell surfacearea—a rate sufficiently high for practical applications. Yet no burningof the carbon takes place.

The fuel cell 200 is refueled by, for example, entrainment of the finecarbon particles 204 into the cell housing 201 in a gas such as carbondioxide or nitrogen in such a manner that the carbon particles 204 areimmediately wetted by the molten salt upon contact and thus wetted,remain in electrical contact with the melt until consumed by anodicoxidation. The system 200 provides a fuel cell configuration into whichcarbon prepared by the methods of this invention may be introduced intothe fuel cell an instantly wetted with ambient molten salt (or moltensalt introduced concurrently) to allow the reaction generating electricpower to take place.

Pretreatment of Carbon Particulates to Enable Contact Wetting—Thepresent invention provides methods of pretreatment of carbon withhydroxide or carbonate materials in the presence of oxygen to render thesurface of such particles chemically altered in a manner that promotesrapid wetting by molten carbonate upon contact between the particles andthe molten carbonate. Such treatment allows the carbon particles to beintroduced into the fuel cell structure of FIG. 1 or FIG. 2 or othermolten-carbonate based fuel cells and batteries and to be wetted uponcontact with resident molten salt or upon contact with molten saltintroduced into the cells concurrently.

The present invention provides a number of methods of producingelectricity in a fuel cell. The methods make it possible to introduceparticulates of highly reactive fuels that are made of substantiallypure carbon into a fuel cell and allow these particles to rapidly becomewetted and begin the electrochemical reaction that produces electricpower.

Method 1—Cold Milling of Carbon Particles and Carbonate Salts. Carbonparticles of size range from 0.1 micrometer to 1 centimeter are mixedwith alkali or alkaline earth carbonate salts at ambient temperatures(or at elevated temperatures below the melting point of the saltmixtures) and ground or milled together in the presence of oxygen (e.g.,from air), using any of the conventional milling techniques. Suchtechniques include but are not limited to ball milling using steel orceramic balls in a rotating drum; high velocity impellers; planetarywheel, ball or roller mills; or hammer mills. The contacting process isshown schematically in FIG. 3. In this configuration 300, a mixture ofcarbon particles and dry salt 302 are introduced into a rotating drum301 together with hard metal or ceramic balls 303, in the presence ofair 304. The action of such milling causes the salt to fuse on thesurface of the carbon particles over microscopic dimensions and flowinto surface defects such as cracks, open pores, or grain boundaries.The precise method used to effect this contacting is of secondaryimportance. The presence of oxygen (as in air) allows some degree ofoxidation at the points of contact between salt and carbon which mayhave short-lived high temperatures allowing partial oxidation of thesurface. The net effect of this milling is to promote the formation offunctional groups such as carboxylate or ester groups on the surface ofthe carbon particle which, when contacting molten salt, are ionized. Theionized surface then allows wetting with the ionized melt because ofsimilar electronic structure.

Method 2—Contacting of Carbon Particles with Molten Alkali Hydroxides inPresence of Oxgyen. Molten alkali hydroxides (LiOH, NaOH, KOH, CsOH) arehighly aggressive agents that, in the presence of atmospheric oxygen,promote the limited oxidation of the carbon surface. Introduction ofparticulate carbon (size range 0.1 micrometer to 1 mm) into molten saltmixtures of one or more of these components promotes the oxidation ofthe carbon surface at a relatively low temperature (<400 C.) in thepresence of air.

FIG. 4 illustrates a method of contacting particles of carbon with themolten alkali hydroxides with concurrent sparging of oxygen (air)through the melt. The method 400 uses a containment vessel of suitablematerial resistant to molten hydroxides. The mixture is stirred with animpellor to promote mixing and contacting with oxygen.

The method 400, as shown in FIG. 4, provides contacting particles ofcarbon with the molten alkali hydroxides with concurrent sparging ofoxygen (air) through the melt 400 using a containment vessel of suitablematerial resistant to molten hydroxides, the carbon and alkali hydroxidemixture 402 is introduced into vessel 401 and sparged with oxygen 404from an immersed tube or conduit 403. The mixture is stirred with animpellor 405 to promote mixing and contacting with oxygen.

Method 3—Exposure of Carbon Particles to Alkali Carbonate Vapors atElevated Temperatures. At the operating temperatures of the fuel cellsdepicted in FIG. 1 and FIG. 2 and of other configurations of a directcarbon conversion fuel cell, the molten carbonate salt will tend todissociate to form metal oxide vapors and carbon dioxide. For example,sodium carbonate will dissociate according to:

-   -   Na₂CO₃=Na₂O+CO₂        If the feed line of carbon particles to the cell is arranged        such that vapors from the molten salt are allowed to flow        through the feed line counter current to the movement of the        carbon particles, then the alkali oxides will deposit onto the        surface of the carbon particles. FIG. 4 illustrates such an        arrangement. Such deposition under slightly oxidizing conditions        will promote the formation of surface functional groups such as        carboxylates, esters, hydroxyl, or quinoidal groups that, upon        contact with molten salts, will tend to ionize. This method does        not require anything other than arrangement of the carbon feed        to allow contacting of the feed particles with the exiting gas        from the fuel cell. The amount of exiting gas allowed to contact        must be controlled to prevent excess losses by Boudouard        corrosion reaction,    -   C+CO₂=2CO,        and consequent loss of energy by consumption of the carbon. This        may be done by dividing the exit gas flow (predominately CO₂        with trace alkali oxides) between feed and exhaust pipe, to        limit the amount of CO2/oxide vapor that is allowed to contact        the incoming carbon particles.

Referring again to FIG. 2, part of the exhaust carbon dioxide form thecell exits the cell through channel 203 and contacts the incoming streamof carbon 204 (un mixed with salt) to provide the desired changes tofunctional groups and wetability. The balance of the exhaust carbondioxide exits through the vent, 214. The relative amounts of carbondioxide exiting through 214 and 203 need to be controlled so thatexcessive amounts of carbon dioxide are not allowed to contact thecarbon; this would promote fuel loss through the Boudouard reaction,described above. The oxygen adsorbed on the carbon (being exposed atsome time to air) is sufficient to provide the necessary oxidation topromote the formation of ionized functional groups.

Referring to FIG. 5, an arrangement of fuel cell and exiting vapors fromthe molten salt in the fuel cell to allow contacting between the saltvapors and the incoming carbon particles is shown.

It is clear that the same pretreatment of the carbon particles may beachieved by passing an inert gas over molten carbonate at 700-850 C, andthence through the particle bed comprised of carbon particles. Thistechnique is an obvious extension of that described in FIG. 5, andforgoes the use of the latent heat of the fuel cell to promote thedissociation of the carbonate and the formation of a gas phasecontaining oxide species.

The system is designated generally by the reference numeral 500. Thefuel cell system comprises a fuel cell body 501, an anode 505 in thefuel cell body 501, a cathode 506 in the fuel cell body 501, a moltenmixture of alkali metal or alkaline earth metal carbonates electrolyte502 in the fuel cell body 501, and a carbonaceous fuel 504 in the fuelcell body 501. The fuel cell system 500 produces electricity with amolten mixture of alkali metal or alkaline earth metal carbonates andfinely divided carbon particles. The particulate carbonaceous fuel isintroduced into the fuel cell and produces the direct electrochemicalconversion of carbon into electricity. A particulate carbonaceous fuelis prepared by finely dividing carbon particles and mixing the carbonparticles with an electrolyte comprising a molten mixture of alkalimetal or alkaline earth metal carbonates.

The system 500 provides a direct carbon conversion fuel cell thatgenerates electric power from the electrochemical reaction of carbon andatmospheric oxygen. A slurry or wetted aggregation 502 is introducedinto the fuel cell housing 501 through port 515. The slurry 502comprises carbon particles 504 immersed in a molten-salt electrolyte503.

The carbon 504 is in the form of finely divided particles, size 10-1000micrometers, having a reactive nano-structure called “turbostratic.” Thecarbon particles are wetted by a molten-salt electrolyte 503 consistingof a mixture of molten alkali carbonates (LiK,Na)2C03 to form a slurry,dense paste or wetted aggregation of particles.

The molten salt electrolyte 503 provides a continuous electrolyte ofcarbon particles 504 between the porous nickel plate anode currentcollector 505 and a porous nickel plate cathode 506. An inert ceramicseparator 507 (e.g., woven or felted alumina or zirconia fibers)saturated with the molten salt is located between anode 505 and cathode506. The anode current collector 505 and the cathode 506 produce anelectrical current 508 in a circuit 509 that extends between anode 505and cathode 506. The electrical current 508 is used to power a device510 within the circuit 509.

The carbon particles 504 can be distributed pneumatically to individualcells, such as cell housing 501, by a small amount of carbon dioxide fedback to the cell from the continuously produced carbon dioxide stream.The pneumatic transport of carbon particles through complex equipment isa widespread industrial practice. The carbon particles 504 and oxygen(ambient air) are introduced as fuel and oxidizer, respectively. Theslurry 502 formed by mixing the carbon particles 504 with moltencarbonate 503 constitutes the anode. The anode reaction is carbon andcarbonate ions forming carbon dioxide and electrons. At the cathode 506,which is similar to that used in other high-temperature fuel cells,oxygen, carbon dioxide, and electrons from the anode form carbonateions. The porous ceramic separator 507 holds the melt in place andallows the carbonate ions to migrate between the two compartments.

Excess electrolyte may drain and flow through port 511 where it isstored as a liquid 512 in a sump 513. By capillary forces, the liquid inthen sump may exchange with that in the slurry by flow backwards throughport 511. The system 500 provides a tilted electrochemical cell topromote rapid draining of excess electrolyte.

The fuel cell system 500 reactions are as follows:

-   -   a. C+2CO₃ ²⁻=3C02+4e− anodic half-reaction, at an inert (e.g.,        Ni) current collector    -   b. O₂+2C0₂+4e−=2C0₃ ²⁻ cathode half-reaction, at a Ni0-coated Ni        cathode    -   c. C+02=C02 Net cell reaction, sum of the half reactions

The fuel cell 500 uses aggregates of extremely fine (10- to1,000-micrometer-sized) carbon particles 504 distributed in a mixture ofmolten lithium, sodium, or potassium carbonate at a temperature of 650to 850° C. The overall cell reaction is carbon and oxygen (from ambientair) forming carbon dioxide and electricity. The reaction yields 80percent of the carbon-oxygen combustion energy as electricity. Itprovides up to 1 kilowatt of power per square meter of cell surfacearea—a rate sufficiently high for practical applications. Yet no burningof the carbon takes place.

Method 4—Use of Chemical Oxidants in the Pretreatment of Carbon Fuels.As described earlier, method 2 provides the activation of carbonparticles by exposure to molten alkali or alkaline earth hydroxides withsufficient oxygen to promote oxidation of the carbon surface andformation of ionizable functional groups. The same oxidation may occurwith the use of other oxidizing agents such as, for example, nitrates.If a small quantity of nitrate is mixed with hydroxide, the resultantmixture will tend to oxidize the surface of the carbon. Pure moltennitrate should not be mixed with particulate carbon, as an explosivemixture will result. If the concentration of sodium nitrate in sodiumhydroxide is maintained below 10%, the molten salt will supportoxidation but not rapid combustion or explosion.

The present invention is useful for carbon fuels comprised ofessentially pure carbon, that has not previously been subjected tooxidation. Such carbon materials include: acetlyene black, variouscarbon blacks and furnace blacks, and the carbons formed bydecomposition of hydrocarbon gasses and oils. The techniques describedabove are also useful in the pretreatment of aerogels and xerogelsderived from thermal decomposition of the green aerogels made by basecatalyzed condensation of formaldehyde and recorcinol, etc.

Referring now to FIG. 6, another embodiment of a fuel cell systemconstructed in accordance with the present invention is illustrated. Thesystem is designated generally by the reference numeral 600. The system600 comprises a fuel cell housing 601 containing an anode 605 and acathode 606. Carbon particles 604 are introduced into the top of thefuel cell fuel cell housing 601. The carbon particles 604 are in theform of finely divided particles, typical size 10-1000 micrometers,having a reactive nano-structure called “turbostratic.” The carbonparticles are immersed in a molten-salt electrolyte 603 consisting of amixture of molten alkali carbonates (Li,K,Na)₂C0₃ to form a paste,slurry or wetted aggregation of particles, 602.

The paste, slurry, or wetted aggregation of carbon particles 602 isintroduced into the top of the fuel cell fuel cell housing 601. Thepaste, slurry, or wetted aggregation of carbon particles 602 comprisesthe carbon particles 604 immersed in the molten-salt electrolyte 603which are introduced into the anode chamber 614 part of the cell. Aninert ceramic separator 607 (e.g., woven alumina or zirconia fibers)saturated with the molten salt is located at the bottom of the anodechamber 614 and separates anode 605 from cathode 606. The inert ceramicseparator 607 saturated with the molten salt is located below anodecurrent collector 605. Gravity helps the flow of the paste, slurry, orwetted aggregation of carbon particles 602. The molten salt electrolyte603 provides a continuous electrolyte between the porous nickel plateanode current collector 605 and a porous nickel plate cathode 606. Thesystem 600 provides a direct carbon conversion fuel cell that generateselectric power from the electrochemical reaction of carbon andatmospheric oxygen.

The anode current collector 605 and the cathode 606 produce anelectrical potential between the anode lead 608 and the cathode lead609, from which electrical current may be drawn by closing the circuitthrough a load (not shown). The fuel cell also provides ports forintroduction of air plus carbon dioxide 610 and exhaust of air andunreacted carbon dioxide 611. The fuel cell also provides at least oneport for exhaust of carbon dioxide reaction product, 612, from the anodechamber; and for the draining of excess molten carbonate from the anodechamber (or introducing additional molten carbonate into the system),designated by 613.

The fuel cell system 600 reactions are as follows:

-   -   C+2CO₃ ²⁻=3C0₂+4e− (anodic half-reaction, at an inert current        collector)    -   O₂+2C0₂+4e−=2C0₃ ²⁻ (cathode half-reaction, at Ni0-coated Ni        cathode)    -   C+0₂=C0₂ (Net cell reaction, sum of the half reactions.)

The fuel cell 600 uses aggregates of fine (10- to1,000-micrometer-diameter) carbon particles 604 distributed in, forexample, a mixture of molten lithium, sodium, or potassium carbonate ata temperature of 650 to 850° C. The overall cell reaction is carbon andoxygen (from ambient air) forming carbon dioxide and electricity. Thereaction yields 80 percent of the carbon-oxygen combustion energy aselectricity—approximately 7.2 kWh/kg-carbon. It provides typically up to2 kilowatt of power per square meter of cell surface area—a ratesufficiently high for practical applications. Yet no direct combustionof the carbon takes place. Electrochemical losses within the cell alsoproduce nearly 2 kWh of thermal energy that is evolved as waste heat.

The fuel cell 600 is refueled by, for example, entrainment of the finecarbon particles 604 into the cell housing 601 in a gas such as carbondioxide or nitrogen in such a manner that the carbon particles 604 areimmediately wetted by the molten salt upon contact with the ambientmolten salt within the anode chamber, and thus wetted, remain inelectrical contact with the melt until consumed by anodic oxidation.

The system 600 has uses in efficient electric power generation and inbroad mobile, transportable and stationary applications. The system 600also has uses in electric power generation at high efficiencies fromcoal, petroleum derived fuels, petroleum coke, and natural gas. Thesystem 600 can help to conserve precious fossil resources by allowingmore power to be harnessed from the same amount of fuel, can helpimprove the environment by substantially decreasing the amount ofpollutants emitted into the atmosphere per kilowatt-hour of electricalenergy that is generated, and can help decrease emissions of carbondioxide, which are largely responsible for global warming.

Direct carbon conversion fuel cells provide a method of producingelectricity in a fuel cell having an anode and a cathode currentcollector, an anode fuel consisting of particulates of carbon wetted orcontacted with molten salt (mixtures of alkali or alkaline earthcarbonates at temperatures above their melting point), and a means offlowing air adjacent to the cathode current collector, this collectorbeing a high surface are porous metal structure made of, for example,sintered nickel particles coated with lithium-doped nickel oxide;silver, copper, gold or other metal providing for the electrochemicalreduction of atmospheric oxygen.

The particulate carbon fuels introduced into the fuel cell must becomewetted with the molten salt. For some carbon fuels (such as raw coal,petroleum coke, and coked or devolatilized coal), the surfaces arecovered with chemical functional groups such as carboxylates, esters,quinoidal, or hydroxyl groups. These groups are readily ionized in thepresence of molten salts. In the ionized state, they are chemicallycompatible with the molten salt and are therefore readily wetted by thesalt upon contact between the particles and the molten salt resident inthe fuel cell.

Other particulate carbon fuels include very pure carbons such as, forexample, (1) very pure carbons produced by pyrolysis of hydrocarbons(such as, for examples, fuel oil, methane, ethane, propane and higherstraight or branched alkanes); (2) acetylene black; (3) furnace blacksand carbon blacks; (4) the thermal decomposition products of anysaturated hydrocarbon alkane, alkene or alkyne; and (5) carbon aerogelsmade by thermal decomposition of the base-catalyzed condensationproducts of resorcinol with formaldehyde. The surfaces of these verypure materials may tend to be free of ionizable functional groups.Therefore wetting will not readily occur upon contact between the carbonand the molten carbonate salt.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A fuel cell apparatus, comprising: a fuel cell body having an upperportion, sides, a bottom portion, and an interior, finely divided carbonparticles of ten to one thousand micrometer-diameter, molten lithium,sodium, or potassium carbonate, wherein said finely divided carbonparticles are distributed in said molten lithium, sodium, or potassiumcarbonate to form an electrolyte, an opening structure in said upperportion of said fuel cell body that allows said finely divided carbonparticles distributed in said molten lithium, sodium, or potassiumcarbonate to be introduced into said interior of said fuel cell body, agas containing oxygen, an opening structure in said upper portion ofsaid fuel cell body that allows said gas containing oxygen to beintroduced into said interior of said fuel cell body, a tilted anodestructure that extends between said sides of said fuel cell body, atilted cathode structure that extends between said sides of said fuelcell body, a tiled inert ceramic separator structure that extendsbetween said sides of said fuel cell body, wherein said tiled inertceramic separator structure is positioned between said tilted anodestructure and said tilted cathode structure, and a drain and flowthrough port structure in one of said sides of said fuel cell bodyadjacent said tiled inert ceramic separator structure, wherein saiddrain and flow through port structure allows said finely divided carbonparticles distributed in said molten lithium, sodium, or potassiumcarbonate electrolyte to drain to said bottom portion of said fuel cellbody.
 2. The apparatus of claim 1 wherein said finely divided carbonparticles are derived from carbon fuels.
 3. The apparatus of claim 2wherein said carbon fuels comprise raw coal or petroleum coke or cokedcoal or devolatilized coal or fuel oil or methane or ethane or propaneor alkanes or acetylene black or furnace blacks or carbon blacks orcarbon aerogels or mixtures of said raw coal or petroleum coke or cokedcoal or devolatilized coal or fuel oil or methane or ethane or propaneor alkanes or acetylene black or furnace blacks or carbon blacks orcarbon aerogels.
 4. The apparatus of claim 1 wherein said finely dividedcarbon particles distributed in said molten lithium, sodium, orpotassium carbonate to form an electrolyte comprises a mixture of moltenlithium, sodium, or potassium carbonate at a temperature of 650 to 850°C. and said finely divided carbon particles.
 5. The apparatus of claim 1wherein said finely divided carbon particles comprise finely dividedcarbon particles having a turbostratic nanostructure.
 6. The apparatusof claim 1 wherein carbon dioxide is produced in said interior of saidfuel cell body and including structure for allowing said carbon dioxideto be removed from said fuel cell body.
 7. The apparatus of claim 1wherein said opening structure in said upper portion of said fuel cellbody that allows a gas containing oxygen to be introduced into saidinterior of said fuel cell structure comprises structure that allowssaid finely divided particles of carbon to come into contact with saidmolten lithium, sodium, or potassium carbonate with concurrent spargingof oxygen.
 8. The apparatus of claim 1 including an impellor in saidinterior of said fuel cell body to promote mixing and contacting withsaid oxygen.
 9. An apparatus, comprising: fuel cell means, said fuelcell means including a fuel cell body having an upper portion, sides, abottom portion, and an interior, carbon particle means for introducingfinely divided carbon particles into said fuel cell means, said carbonparticle means comprising finely divided carbon particles of ten to onethousand micrometer-diameter, molten lithium, sodium, or potassiumcarbonate, wherein said finely divided carbon particles are distributedin said molten lithium, sodium, or potassium carbonate to form anelectrolyte, an opening structure in said upper portion of said fuelcell body that allows said finely divided carbon particles distributedin said molten lithium, sodium, or potassium carbonate to be introducedinto said interior of said fuel cell body, oxygen means for introducinga gas containing oxygen into said fuel cell means, said oxygen meansincluding a gas containing oxygen and an opening structure in said upperportion of said fuel cell body that allows said gas containing oxygen tobe introduced into said interior of said fuel cell body, a tilted anodestructure that extends between said sides of said fuel cell body, atilted cathode structure that extends between said sides of said fuelcell body, a tiled inert ceramic separator structure that extendsbetween said sides of said fuel cell body, wherein said tiled inertceramic separator structure is positioned between said tilted anodestructure and said tilted cathode structure, and a drain and flowthrough port structure in one of said sides of said fuel cell bodyadjacent said tiled inert ceramic separator structure, wherein saiddrain and flow through port structure allows said finely divided carbonparticles distributed in said molten lithium, sodium, or potassiumcarbonate electrolyte to drain to said bottom portion of said fuel cellbody.
 10. The apparatus of claim 9 wherein said finely divided carbonparticles are derived from carbon fuels comprising raw coal or petroleumcoke or coked coal or devolatilized coal or fuel oil or methane orethane or propane or alkanes or acetylene black or furnace blacks orcarbon blacks or carbon aerogels or mixtures of said raw coal orpetroleum coke or coked coal or devolatilized coal or fuel oil ormethane or ethane or propane or alkanes or acetylene black or furnaceblacks or carbon blacks or carbon aerogels.